Welding machine having provision for precise positioning of two or more workpieces relative to one another during high-speed welding operations

ABSTRACT

A welding machine for welding attachments to base members on a high speed production bases and wherein provision is made for rapidly feeding one or more of the attachments relative to each base member and for precisely positioning the attachments and base members relative to one another prior to and during a welding operation.

United States Patent [45] Patented 73] Assignee [54] WELDING MACHINEHAVING PROVISION FOR PRECISE POSITIONING OF TWO OR MORE WORKPIECESRELATIVE TO ONE ANOTHER DURING HIGH-SPEED WELDING OPERATIONS 11 Claims,29 Drawing Figs.

[51] Int.Cl B23k11/10: H0 1 h 3/ l 6 [50] Field of Search 219/79, 80,103, 93; 198/19, 33, 232; 200/61.42

[56] References Cited UNITED STATES PATENTS 2,304,825 12/ 1 942Hothersall 219/64 2,618,725 11/1952 Renard 219, 80 2,681,968 6/1954Renard..... 219/80 2,695,941 11/1954 Treff 219/80 2,500,886 3/1950Torkelson 219/93X 2,623,974 12/1952 Prucha 219/93 Primary Examiner-J. V.Truhe Assistant Examiner-L. A. Schutzman Attorney-Wo1fe, Hubbard,Leydig, Voit & Osann ABSTRACT: A welding machine for welding attachmentsto base members on a high speed production bases and wherein provisionis made for rapidly feeding one or more of the attachments relative toeach base member and for precisely positioning the attachments and basemembers relative to one another prior to and during a welding operation.

PATENTEUJAN 51971 I I 3553419 sum 1 OF 9 VENT W Uscar Gm 'vew.

PATENTEDJAN SIS?! $553,419

SHEET 2 BF 9 CATTOYQNEYW I PATENIEDJAN 5197: 3553.419

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WELDING MACHINE HAVING PROVISION FOR PRECISE POSITIONING OF TWO OR MOREWORKPIECES RELATIVE TO ONE ANOTHER DURING HIGH-SPEED WELDING OPERATIONSCROSS REFERENCE TO RELATED APPLICATIONS The present application is adivisional application based on the copending application of Oscar W.Garver, Frederick E. Ullman, Christian l-I. Stettler and Hans W. Kopp,Ser. No. 463,062, filed Apr. 29, I965now U. S. Pat. No. 3,368,056; suchcopending application having been a divisional application based uponthe then copending application of the same inventors, Ser. No. 180,415,filed Mar. 15, 1962, and issued as U. S. Pat. No. 3,233,072 on Feb. 1,1966; all assigned to the assignee of the present invention.

BACKGROUND OF THE INVENTION The present invention relates to weldingmachines and, more particularly, to machines for welding attachments tobase members. In its principal aspects the present invention isconcerned with improved welding apparatus having provision for preciselyfeeding the attachments relative to the base members so as to insureaccurate positioning of the workpieces during the welding operation.While not so limited in its application, the attachments mayconveniently take the form of ears and the base members may convenientlytake the form of pails.

In the manufacture of metal shipping pails, it is conventional to weldears or projections to the sides of the pail for receiving the ends of awire bail. The ear may be in the form of a cup-shaped stamping having acentral opening for the bail and having lateral projections which seatagainst the side of the pail. Since the pails are commonly made of sheetsteel, it is desirable to protect or decorate the outer surface. eitherby painting or by lithographing which, in addition to providing physicalprotection, often serves to identify the contents, to provide acolorful, attractive appearance, and to carry an advertising message. Itis desirable that the painted or lithographed coating be applied to theside of the pail while it is still flat, prior to welding. Moreover, itis desirable that the coating be continuous, covering all of the surfacearea. This requires that the bail ears be secured after the coatinghasbeen applied, so that any spot welding of the ears must take placethrough the coating. Efforts have been made in the past to weld an earor other attachment to a painted surface by forming, on the attachment,a sharp projection so that when pressure is applied, the projectionestablishes electrical contact to permit flow of welding current.However, it has not been possible to weld through an insulating coatingwith 100 per cent reliability. Consequently, use of this procedure hasbeen limited to containers having thin walls and where the strength ofthe weld has not been an important factor, for example, in the weldingof a key to the lid of a coffee can. One difficulty which has beenexperienced in this type of welding is the flashing which takes placewhen the initial electrical contact is made between the sharp projectionand the base resulting in overheating and destruction of the projection,with inability to complete the weld.

Welding through an insulating coating has been avoided in the case ofshipping pails because of inability to make a consistent weld, becauseof the high degree of strength required in the weld, particularly whenthe pail is to'be filled with a dense, heavy substance, and theinability to properly inspect the weld for soundness.

It is an object of the present invention to provide a welding machinewhich is not only capable of producing a reliable weld but which isextremely rapid, a single machine being capable of processing shippingpails at the rate of 2,400 units per hour or even higher. It is a morespecific object in this connection to provide an automatic machine inwhich the positioning and welding procedure is performed in steps atsuccessive work stations, with the pail being indexed from station tostation and with a plurality of containers being acted uponsimultaneously in the successive stations.

It is still another object of the present invention to provide a weldingmachine which is consistent and accurate in the positioning of the earswith respect to the seam and hence with respect to the printed matter onthe pail. It is a related object to provide a machine for welding pailears in which the ear is not only placed at a desired point on theperiphery but accurately positioned and leveled at a desired height. Itis a more detailed object to provide means for insuring positivePositioning which determines whether the position of the pail is withinpredetermined tolerance and which includes provision for preventing aweld by failure to provide an ear if the tolerance is exceeded. It isanother object related to the foregoing to provide means for detectingthe presence of an car at the welding station and for disabling thewelding gun in the event that an ear is lacking or in the event that anear is improperly positioned.

In a more detailed aspect of the invention, it is an object to provide anovel orienting and feeding apparatus for the bail cars which is capableof feeding them one by one down a feed chute by means of an escapementmechanism timed with the movement of the welding guns and the indexingof the pails from station to station in the machine.

It is yet another object to provide a machine of the above type which iswell suited for heavy industrial use, which may be operated for longperiods of time without maintenance or adjustment and which issubstantially foolproof, permitting safe operation on a high productionbasis even with unskilled or inexperienced personnel.

Other objects and advantages of the invention will become apparent uponreading the attached detailed description and upon reference to thedrawings, in which:

FIG. 1 shows a shipping pail with a bail ear affixed by the presentmachine;

FIG. 1a is an enlarged perspective showing one of the ears;

FIG. 2 is a front elevation of an ear welding machine constructed inaccordance with the present invention somewhat simplified for easyunderstanding;

FIG. 3 is a left-hand elevation of the machine shown in FIG.

FIG. 4 is a diagram showing the linkage for driving the positioningmembers;

FIG. 5 is a fragmentary front view of the machine showing the cams fordriving the transfer and positioning members;

FIG. 6 is a fragmentary perspective showing the ear escapement;

FIG. 7 is a fragmentary section taken along the line 7-7 in FIG. 6;

FIG. 8 is a fragmentary face view in partial section showing the pailorienting mechanism;

FIG. 9 is a fragmentary section taken along line 9-9 in FIG. 8 showingthe first seam detector;

FIG. 10 is a fragmentary section taken along the line 10-10 in FIG. 8showing the seam detector switch;

FIG. 11 is a fragmentary top view of the star wheel employed in thefirst seam detector;

FIG. 12 is a fragmentary section taken along the line 12-12 in FIG. 8and showing the final seam detecting element;

FIG. 13 is a section taken along the line 13-13 in FIG. 2 showing themeans for moving the welding electrodes;

FIG. 14 is a fragmentary section taken along the line 14-14 in FIG. 13showing the electrode advancing means in plan view;

FIG. 15 is a fragmentary section taken along the line 15-15 in FIG. 13showing the electrodes in welding position;

FIG. 16 is an enlarged fragment showing the function of the centeringpin and supporting table;

FIG. 17 is a vertical section taken along line 17-17 in FIG. 14 showingthe opening of the gates to admit the welding electrodes;

FIG. 18 is a perspective of one of the gates,

FIG. 19 is a section taken on the line 19-19 of FIG. 2 showing the earchecking arm;

FIG. 20 is a view similar to FIG. 19 with the parts in a moved position;

FIG. 21 is a simplified schematic diagram of the control circuit;

FIG. 22 is a plot showing the variation in applied force projectionheight and current as a function of time; and

FIG. 23a-23e are enlarged sections of a typical weld at successivepoints in the welding cycle keyed to FIG. 22.

While the invention has been described in connection with a preferredembodiment, it will be understood that we do not intend to limit theinvention to the embodiment shown but intend, on the contrary, to coverthe various alternatives and equivalent constructions included withinthe spirit and scope of the appended claims.

Turning now to FIG. 1 there is shown, inverted, a shipping pail 30 ofwell-known type having a top curl 31, a bottom flange 32 and a seam 33.Located on opposite sides of the pail are bail cars 34, only one ofwhich is visible in the FIG. The machine to be described is primarilyintended for welding such ears in place upon a prepainted orprelithographed pail, although those skilled in the art will appreciatethat it is not limited thereto. While the invention is not limited toany particular form of bail ear, a preferred form of ear (FIG. 1a)includes a cupshaped central portion 35 having a central open ing 36 forreceiving the end of thebail and having tabs 37, 38 for spot welding tothe wall of the pail.

The machine, generally indicated at 50, has a longitudinal frame 51supported on a base 52. Extending upwardly at the rear of the frame arepillars 53, 54 which'supporta superstructure 55 in adjusted verticalposition. Pails 30 enter the machine at the left from an externalconveyor and, as will be described, each pail successively occupies aseries of work stations in which the pails are acted upon. In themachine described, there are a total of six work stations indicated at61-66, respectively, in which the pails are first oriented, then weldedand, finally, tested. For the sake of versatility and for optionalfunctions or specialized purposes, two of the stations, in the presentinstance stations 63 and 66, are idle. It will be understood, however,that the pails pass through the machine at closely spaced sequence sothat all of the stations at any given time have pails positionedtherein.

While the various functions performed by the machine are closelyintegrated, it will, nevertheless, be convenient for easy understandingto discuss the functions of the machine under separate appropriatesubheadings.

PAIL TRANSFER AND POSITIONING MECHANISM In carrying out the presentinvention a longitudinal pail transfer member is provided which extendsunder all of the stations and which reciprocates back and forth througha unit station-to-station distance for the purpose of engaging thedownwardly presented facing edges of the pails and for moving all ofthem simultaneously to the next station. Cooperating with the transfermember is a longitudinally extending positioning member having means formoving the same vertically between a lowered inactive position, at whichtime the pails are engaged by the transfer member, and an upraisedactive position in which the pails are firmly held clear of the transfermember so that the latter is free to make a return stroke. The transfermember in the present instance is in the form of a longitudinallyextending bar 70 mounted on rollers 73, 74 (FIG. 19) for endwisemovement in the machine and having a plurality of pail engaging membersor lugs 71-72 secured to its upper edge. A pair of cams are employed formoving the transfer member in opposite directions. Thus, as shown inFIG. 5, drive cams indicated at 81, 82, mounted on a cam shaft 83 actupon a bellcrank 84 which is pivoted for rocking movement about a shaft85. At its upper end the crank is connected to a link 86 which, in turn,is pivoted to a bracket 87 clamped to the transfer member 70. For thepurpose of driving the cam shaft 83, a motor 90 is used having a speedreduction unit 91.

For the purpose of moving the pails upwardly and clear of the transfermember 70 into a position to be acted upon, a

positioning member is provided having spaced sections 101, 102 whichmove upwardly and downwardly in unison. The positioning member is formedin two longitudinal sections in order to permit separate verticalpositioning of the pail in the welding station as will be discussed indetail.

In order to provide a wide base for positioning purposes, the sections101, 102 have corresponding spaced sections 101a, 101b, 102a and l02bwhich straddle the transfer member 70 as shown in FIG. 3. Means areprovided along the top edge of each section for engaging the lower edgeof the pails. Such means may take the form of lugs 105 or may take theform of rollers in the orienting stations 61, 62 to be discussed. Tounderstand the means for bodily raisingand lowering the positioningmember 100, it will be noted that cams 111, I12, mounted on shaft'83an'd disposed immediately behind the cams 81 and 82 previously.discussed, act upon a cam follower in the form of a bellcrank 114 havinga shaft 115. Connected to the outer end of the bellcrank 114 is apushrod 115 which is pinned to an arm 117 secured to a longitudinallyextending rocker shaft 120 which is journaled at its end in suitablebearings 121. To convert the rocking movement of the rocker shaft 120 tovertical movement of the positioning member, the shaft is provided withlift arms along its length having short links which are coupled to thesections of the positioning member and with radius arms being providedto insure that the elevation is equalized. Thus the shaft 120 has liftarms carrying short links 126 which are connected at their upper ends tobrackets 127 on the section 102a. For the purpose of transmitting equalmovement to the section 102b, the bellcrank shaft 115 has an arm 1140which drives a pushrod 116a pinned to an arm 117a on a rocker shaft 120awhich extends along the rear of the machine. The rocker shaft 120acorresponds to the rocker shaft 120 previously discussed. To elevatesection 102b the pushing member of the rocker shaft 120a has arms 1250which act upon short links 1260 which are connected at their upper endsto brackets 127a along the underside of the member 102b.

It will be apparent, then, that when the cams rotate the members 102aand 1021; will be moved upwardly through equal distances. To insure thatthe members are guided in this upward movement, pairs of swingableradius arms 129 are provided for each of the sections, forming aparallelogram linkage.

While the above structure suffices for elevating the sections 102a, l02bof the positioning member 100, it will be understood that similarstructure is employed for elevating the two sections 101a, l01b and withcorresponding reference numerals being used where applicable.

Since cams 81, 92 which reciprocatethe transfer member and the cams 111,112 which move the positioning member 100 vertically are offset inphase, it will be seen from FIG. 3 that the effect is to advance thepails simultaneously step by step. Taking the first station 61 by way ofexample, when the positioning member 100 is upraised, the lugs on thetransfer member are moved to the left to a position under the enteringpail. When such entering pail, indicated at 30a in FIG. 2, is lowered bythe positioning member, it seats on the lugs 71 and 72. The transfermember 70 then moves to the right until the pail is in the first station61 whereupon the transfer member momentarily comes to rest. Thepositioning member 100, as a result of the cams 111, 112 and the-linkagejust described, moves vertically, lifting the pail clear of the transfermember and in position to be acted upon in the first station. Each ofthe other pails in the series is similarly advanced one'step.

In order to feed a pail into the machine and to remove a pail havingwelded ears from the machine, conveyor chains are provided at both theinput and output. Referring to the input end, a conveyor chain 140,which preferably consists of two parallel sections is trained aboutshafts 141, 142, the shaft 142 being preferably mounted on thepositioning member 100 for movement up and down therewith. For drivingthe conveyor chain 140, a drive chain 143 is provided which is driven bya second chain 144 coupled to the driving motor. A similar setup isemployed at the output, with a conveyor chain 150 being trained aboutshafts 151, 152 and driven by chains 153, 154.

ROTARY ORIENTING MECHANISM In the exemplary apparatus, and as disclosedand claimed in our aforesaid copending application Ser. No. 463,062filed Apr. 29, I965, provision is made at the first station 61 forrotating the pail at relatively high speed to an approximate 62 arerotating mechanisms 161,. 162. Attention will first be given to therotating mechanism 161. The mechanism 161 is mounted upon a downwardlyextending pedestal 163 carrying a cylindrical housing 164 at its lowerend. The housing 161 has an outer shell for an adjusting purpose whichwill become clear as the discussion proceeds. Centered within thepedestal 163 is an input drive shaft 165, and projecting downwardlytherefrom is a disc drive shaft 166. Coupled to the lower end of thedisc drive shaft 166 is a drive disc 170 having a layer of rubber orother friction material 171 on its under surface for engaging thepresented upper edge of a pail 30. Downward pressure is exerted upon thedisc 170'so that the disc seats firmly against the pail by means of aresilient connection 172 which is interposed between the drive shaft 166and the disc. The resilient connection 172 is preferably in the form ofa resilient spider, a construction well-known to those skilled in theart.

For the purpose of controlling rotation of the disc, a clutch 175 isinterposed between the input shaft 165 and the output shaft 166 and, tobring the output shaftto a stop on the plate when the clutch isdisengaged, anelectri'c brake 176 is provided. The combined clutch andbrake together form a commercially available unit. To supply rotativepower for the input shaft 165, to rotate the same at a speed ofapproximately 50 r.p.m., a reduction drive is provided which includes adrive motor 180, a right-angled stepdown connection 181 having adownwardly extending output shaft 182. Mounted on the shaft 182 is aspur gear 183 which meshes with a spur gear 184 at the upper end of theshaft 165. In order to permit rotation of the pail under the urging ofthe drive disc 170, rollers 185, which may be made of nylon or the like,are mounted along the upper edge of the positioning member 100.

In order to detect the arrival of the pail seam at a predeterminedpoint, and to deenergize the clutch and energize the brake when thisoccurs, a detector is provided in the form of a sharp edged member whichis biased against the side of the pail and which operates an associatedswitch when the sharp edge is engaged by the seam. Turning to FIGS. and11 the detector element is in the form of a star wheel 190 mounted upona shaft 191 carrying a cam 192 at its upper end for operating a switch193. The shaft, as shown in FIG. 9, is mounted in a carrier 195. Forbiasing the carrier in the direction of the pail, the carrier is mountedupon a lever 196 which is pivoted at its upper end 197 and which isengaged by a coil spring 198. Thuswhile the pail rotates, the star wheel190 presents an edge 1900 in the path of movement of the seam 33 on thepail. It will be understood by one skilled in the art that even where aflush-type seam is employed, nevertheless, there is a narrow rathersharply defined groove on the surfaceof the pail capable of engagementby the star wheel. When the seam rotates to the position shown in FIG.11, the point 1900 of the star wheel enters the seam groove causing thestar wheel to step one step in the counterclockwise direction. The cam192 at the upper end of the star wheel shaft thereupon actuates theswitch 193 which, through the control circuit to be described, serves todisengage the clutch and energize the brake to bring the pail to a stop.

Means are provided for retracting the seam detector to an upper,out-of-the-way position during station-to-station transfer and forlowering the detector when a pail is in the orienting station. Tounderstand the retracting means reference is made to FIGS. 3, 8 and 9.It will be noted that the detector assembly is not rigidly secured tothe housing of the rotating mechanism, but, instead, is mounted upon avertical slide 210 which engages way surfaces 211 secured to the housingmember outside of the housing 161. For moving the slide 210 upwardly anddownwardly, a positioning collar 215 is provided which surrounds thepedestal 163 and which is slidable thereon. Formed in the lower portionof the collar 215 is an annular groove 216 which is engaged by a roller217 pinned to the slide 210. Thus, it will be apparent that when thecollar is raised, the slide 210, and the detector assembly secured toit, is also raised, this condition being illustrated in FIG. 9. For thepurpose of moving the collar 215 upwardly during each transfer cycle, alinkage is provided which is operated by the rocker shaft 120. Suchlinkage includes an arm 220 (FIG. 3) 3) which is connected to a push rod221 operating a bellcrank 222. Motion is transmitted from the bellcrank222 to a second or intermediate bellcrank 223 by a parallelogram linkagemade up of links 224, 225. Motion is transmitted from the bellcrank 223to a final bellcrank 226 which is rotatable about a shaft 227 via asecond parallelogram linkage made up of parallel links 228, 229. For thepurpose of transmitting the rocking movement of the shaft 227 to thecollar 215, arms 231, 232 (FIG. 8) are secured to the shaft, carryingrollers 233, 234 at their forward ends which ride in an annular groove235 at the upper end of the collar.

Provision is also made for camming the detector radially outward awayfrom the pail as it is upraised for the purpose of clearing the flangeat the end of the pail and the drive disc which engages it. In FIG. 9 itwill be noted that the springbiased arm 196 which carries the detectorelement has a roller 240 which rides on the surface of the way 211 andacts as a cam follower. Thus, when the detector is drawn upwardly, theroller 240 rides up on the way swinging the detector outwardly.Conversely, when the collar 215 is lowered the roller 240 reaches thelower end of the way 211 providing drop off so that the spring 198 iseffective to bias the detector element against the side of the pail.

It will be apparent, then, that upon rotation of the rocker shaft in onedirection the detector will be moved downwardly and inwardly intocontact with the pail and, upon movement in the other direction, i.e.,during transfer, the detector will be moved outwardly and upwardly to anout-of-theway position. Because of the dual parallelogram linkage justdescribed, it is possible to adjust the height of the superstructure 55to accommodate pails of different heights, without necessity forreadjusting the angling of the collar actuating arms 231, 232. Thesuperstructure adjusting means will be covered at a later point.

For the purpose of limiting maximum rotation of the pail to less than itwill be understood that a duplicate of assembly having a switch 244 isprovided in a diametrically opposite position (see FIG. 3). As will beobserved in the control diagram FIG. 21, operation of the switch ineither of the detector assemblies suffices to terminate rotation of thepail. Stopping the pail at either of two 180 positions is permissiblesince the ears to be welded to the pail are fixed in symmetrical 180positions. For the purpose of simultaneously positioning the detectorassemblies 190, 1900, the associated way elements are secured to anouter shell 245 of the orienting drive housing 161. A manually operatedclamping screw 246 serves I to clamp the outer shell 245 and the twodetector assemblies in any position depending upon the desired positionof the bail ears.

The net effect of the orienting mechanism in the first station 61 is toproduce approximate orientation of the pail, say,

the pail is in the station. The degree of overtravel after cutoff is tosome extent dependent upon whether the pail has been rotated to a largeangle or a small angle prior to cutoff.

In the illustrative apparatus, means rotating at a substantially slowerspeed are provided in the second station in order to achieve final andexact positioning. Since the orienting mechanism employed in the secondstation is a substantial duplicate of that in the first, except for thespeed of rotation and the construction of the detector element,corresponding reference numerals have been employed to identifycorresponding parts with addition of subscript a. To achieve. a slowerspeed, on the order of 6 r.p.m., a stepdown ratio has been employed inthe gears 183a, 1840, as contrasted with the step-up ratio in the gears183, 184-in the companion unit. With regard to the construction of theslow speed detector, the element, indicated at 250 in FIG. 12, has asharp detecting 'edge 251 and is mounted upon a parallelogram linkagewhich includes links 252, 253. The link 253 is connected to a verticallyextending shaft 254 which controls switches 255, 256. The switch 255 isso adjusted as to operate immediately upon the sharp edge 251 beingengaged by the seam whereas the switch 256 is adjusted to operate onlyafter a predetermined amount of overtravel. The effective spacing"between the switches 255, 256 determines the positional tolerance, i.e.,as long as the orientation is within prescribed limits, an ear will bewelded to the pail. However, and as covered in the later section, in theevent that the switch 256 is operated, indicating that the tolerance isexceeded, provision is made for preventing a weld so that the pail maybe removed from the production line and inserted again at the input sideof the machine.

Moreover, means are provided for registering the number of successivepails which are outside of the tolerance, i.e., without ears, and forsounding an alarm or shutting off the machine when a predeterminednumber has been exceeded, all as later covered in detail.

. Using the above construction, with approximate and exact orientationin successive stations, orientation may be achieved within a peripheraltolerance on the order of 0.080 inch consistently and at high speed.Upon subsequent lowering of the pail by the positioning member, the pailis advanced into the next station 63. This station, in the presentconstruction, is an idle one in that no operation is performed upon thepail. However, this station contributes to the versatility of themachine in that any desired operation, requiring an oriented pail, maybe performed at this point. For the purpose of holding the pail securelyin station 63 when it is upraised by the positioning member, astationary disc 260 is provided mounted upon a plunger 261 which istelescoped into a bushing 262. A coil spring 263 interposed between thebushing and the disc biases the disc downwardly.

POSITIONING OF PAIL AND EARS IN WELDING STATION IN ACCORDANCE WITH THEPRESENT INVENTION Means are provided within the welding station 64 foraccurately positioning bail ears on opposite sides of the oriented pailin position to be acted upon by the welding guns. Prior to describingthe ear positioner, consideration may be given to the means employed forpositioning the pail at a proper height. It is one of the features ofthe illustrative welding machine that a separate adjustable positioneris provided in the welding station to enable variation in the height ofthe car on the pail and as necessary to avoid reinforcing beads whichmay be formed in the wall of the pail. Thus, there is provided, as shownin FIG. 5, a vertical positioning member 280 which is mounted forvertical movement on vertical ways 281, 282.

A linkage connects the positioning member 280 to the rocker shaft 120 sothat the movement is coordinated and timed with the movement of thetransfer member 70 and positioning member 100 previously discussed. Thislinkage in the present instance includes an arm 283 which is secured tothe rocker shaft and which is connected to a bellcrank 284 having apivot point 285. A second bellcrank 286 has a pivot point 287. Means areprovided forvarying the effective point of connection between thebellcranks 284,286. In the present instance this is accomplished byproviding a pivot block 288 in the bellcrank 286 with an adjusting screw289 for adjusting the throw. It will be apparent that the adjustment 289enables the positioning member 280 toreach any desired height at the topof the stroke at which pointth eears are affixed.

For the purpose of holding the drum'in position in the welding station,a disc 290 is mounted upon a shaft 291 slidable in the bushing 292, withthe disc being urged downwardly by means of a coil spring 293surrounding the shaft.

,Attention will next be given means for depositing an car on each sideof the pail timed with tlieadvancement of a pail into the weldingstation. For the purpose of orienting the ears to face the pail, anorienting device 300 (FIGSL'2 and 3) is employed having downwardlyextending chutes 301, 302 respectively. The orienting device does notper se form a part of the present invention and it will be understoodthat any suitable orienting arrangement, taken from the prior art, maybe employed. Moreover, it will be understood that conveyor means, forexample, of the magnetic belt-"type,*may be provided for elevating theears from a bulk source to the orienting device 300. Since thefeedingarrangem'ents for the two sides of the pail are identical,attention maybe focused upon that visible at the front of the machine asbest illustrated in FIGS. 6'and 7. At the lower end of the chute 301 isan escapement 310. The escapement includes a rocking assembly 311 whichis oscillated about a pivot 312 by means of a link 313 which isconnected to solenoid operators having input coils 314, 314a. For thepurpose of accepting an car from thechute 301 at one end of the strokeand for releasing the-"earat the otherend of the stroke, the escapementmember 311 includes a flat leaf spring member 317 having a retainingforward edge'3l8 mounting a cam follower 319 which cooperates with astationary cani surface 320. It will be apparent that with an ear in theposition shown in FIG. 6, clockwise rotation of the escapementwill causethe cam follower 319 to approach the cam 320. When engagement takesplace, the cam follower is cammed laterally bending the leaf spring 317so that the edge 318 thereof moves out of the way of the ear, whereuponthe ear is permitted to fall through a final vertical slide chute 321.Preferably, the sides of the chute 321 are grooved as indicated at 322so that the ear is positively guided in its downward movement. Theescapement member includes an obstructing face indicated at 325 whichholds the next succeeding ear, indicated by the dotdash outline, in theposition shown until the escapement member has fully retracted,whereupon such ear drops into place in readiness for a subsequentdischarge cycle. Control circuits for energizing the coils 314, 314a ofthe solenoid will be discussed in detail in connection withconsideration of FIG. 21. It will suffice for the present to say thatreload of the escapement is disabled whenever the pail is not in properorientation, i.e., whenever the switch 256 is actuated indicating thatthe positional tolerance has been exceeded.

In accordance with the present invention, and as best illustrated byreference to FIGS. 13--17 conjointly, means-defining a supporting tableare provided for catching the car as it descends down the final chute321 and for supporting the ear at the proper height in horizontalposition. Moreover, means including a tapered positioning pin areprovided for entering the bail opening and for precise final centeringof the ear just prior to engagement by the welding electrodes. Thus,there is provided at the welding station a locating table 330 and atapered centering pin 331 with means for bringing them into operationsequentially. Sequential operation is brought about by mounting both ofthe elements on a vertically arranged positioning arm 332 having anupper horizontal axis 333 and by providing a resilient mounting to holdthe table in projecting position. Thus, in the present instance thetable 330 has a mounting block 334 which is slidable on a rearwardlyprojecting rod 335 and which is biased to a forward position by a spring336. Accordingly, as the centering arm 332 is swung forwardly, i.e., inthe direction of the pail, the table 330 first engages the wall of thepail to provide a positive stop for the advancing bail car 34. Uponcontinued inward movement of the arm 332, the tapered centering pin 331enters central opening 36 in the ear so that the ear centers itself withrespect to the pin. Since the pail is rotationally oriented with respectto the machine, and since the ear is thereby positioned with respect tothe machine while being held horizontal, it will be apparent thatprecise location of the ear on the side of the pail is assured. Meansare provided for swinging the positioning arm timed with the movement ofthe welding guns as covered in the following section.

CONSTRUCTION AND ACTUATION OF WELDING GUNS In the welding station twoseparate welding gun assemblies 350 are provided, one at the front ofthe machine and one at the back, each consisting of two sets ofelectrodes so that both of the ears are welded simultaneously. Since thetwo assemblies are substantially identical, detailed. attention may begiven to the assembly at the front of the machine. In the exemplarywelding system, the piece to be welded is provided with a sharpprojection at each point of welding for penetration of a protective, orinsulating coating on the pail, and means are provided for advancing thewelding electrodes by positive mechanical action to develop a forcesufficient to cause penetration of the coating by the projectionfollowed by substantial collapse of the projection before weldingcurrent is applied, thereby to produce a sound weld free of any tendencytoward flashing, or burning away, of the projections. To

' make the two welds, the welding assembly 350 has two welding guns 351,352. The first gun 351 is mounted on a bracket 353 secured to a frame354. The bracket is of C shape having guide portions 355, 356. Mountedfor sliding movement in the bracket is a cylindrical electrode carrier357 mounting a rod 358 which projects forwardly, carrying an electrode359 having a terminal 360.

The second gun 352 is mounted in a bracket 363-having ends 365, 366 fortheslidable mounting of a cylindrical electrode carrier 370 having a rod368 terminating in an electrode 369 and terminal 370a. The returncircuit for the electrodes 369, is completed through a relativelystationary electrode 37].

Means are provided in the present construction for cyclically retractingthe electrode 371 downwardly so that it is out of the way of a pailbeing advanced into the welding station and for then moving theelectrode upwardly to a position within the pail after the pail comes torest. In the present instance this is accomplished by mounting thereturn electrode 371 at the end of an electrode arm 375 which is pivotedto the base 354 upon a shaft 376. Extending downwardly from the arm 375is a drop link 376a which is connected to an arm 377 mounted on therocker shaft 120. [twill be apparent that when the rocker shaft-rocksduring the transfer portion of the cycle, the arm 375 and its electrode371 are swung downwardly clear of the advancing pail and swung upwardlyagain to the position shown when the pail is clamped in the weldingstation.

Means including a stiff preloaded spring are provided for positivelyadvancing the welding electrodes and for maintaining the electrodesclamped securely against the ear prior to, and during, the weldingcycle. Thus, referring to FIG. 14, a spring 380 is mounted within thecylindrical carrier 357 surrounding the rod 358. The rod is formed withan enlargement 381 which is normally seated in a recess 382 formed inthe forward end of the cylinder. The spring is compressed at its rearend by a preload adjusting member 385 which is in the form of a bushingthreaded into the end of the cylinder 357, the bushing having a centralbore 386 for clearing the rod 358. lt will be apparent, then, that whenthe bushing 385 is screwed into the end of the cylinder, the spring iscompressed to exert a substantial force, which in a practical case maybe on the order of 350 lbs. against the enlargement 381 on the rod.

Thus, when the carrier cylinder 357 is advanced forwardly, and theelectrode strikes the workpiece, there is an immediate buildup of forceagainst the workpiece until the force is sufficient to lift the rod fromits seat 382 against the force exerted by the preloading spring. Aspring pressure of at least the value of the preload then continues tobe exerted against the workpiece during the remainder of the weldingcycle. It will be understood that an identical preloaded springarrangement is included within the cylinder 367 associated with thecompanion welding electrode. 1

For the purpose of advancing the electrode carriers with positivemechanical action for complete overcoming of inertial effects, ascontrasted with the nonpositive action of an air cylinder or the like, adriving linkage is employed including a cam and overdriven cam followerdriven by the cam shaft 83. Thus, there are mounted on the shaft 83 apair of earns 39], 393 which cooperate with a cam follower lever 393a toreciprocate a vertical link 394. The latter drives a bellcrank 395 whichis mounted for rocking about a shaft 396. The upwardly extending portion397 of the bellcrank is pinned to the reciprocating bar 398. For thepurpose of insuring substantially pure reciprocation, a second verticallink 399 is provided which is pivoted on the shaft 326 and which servesto complete a parallelogram. In short, rotation of the cam shaft causesthe bar 398 to reciprocate'backwardly and forwardly. For the purpose ofcoupling the reciprocating bar to the electrode mounting cylinders,short links 401, 402 are provided in the form of tumbuckles which aresecured at their forward ends to the bar 398 and which are connected attheir rear ends to clamps 403, 404 respectively which grippinglyencircle the two cylinders. The walls of the cylinders may be grooved asnecessary to accommodate or clear the rear ends of the links 401, 402.

In accordance with one of the detailed features of the presentconstruction, gates are provided at the lower end of the chute 321 forthe purpose of guiding an ear dropped by the escapement 310, to weldingposition together with means for moving the gates out of the way of theadvancing electrodes 359, 369. Thus referring to FIGS. 17 and 18, twogates 41], 412 are provided having longitudinal grooves 413, 414 whichserve to guide the ends, or welding tabs, on the car 34. The grooves413, 414, with the gates in normal position, are aligned withcorresponding grooves in the chute 321. To mount the gates for outwardswinging movement they are pivoted upon pins 415, 416 respectively. Thegate 411 is held closed by a coil spring 421. The spring is mounted on apushrod 422 which is guided at its upper end at 423 and which is pinned,at its lower end, to an arm 424 on the gate. The normal or closedposition of the gate is defined by engagement of stop surfaces at 425. Acorresponding spring 431 on a rod 432 serves the same purpose for thegate 412. In order to swing the gate apart a cam and cam followerareinterposed between the gate and the centering arm 332 which carries thecentering pin 331 previously discussed. Thus, there is'provided on thecentering arm transversely positioned cam plate 440 engaging cam rollers441, 442 mounted on the gates 411, 412 respectively.

Attention may next by given to the means employed for swinging thecentering arm 332 to insure that it is timed with respect to theadvancement of the electrodes. As shown best in FIG. 13, such arm iscoupled to the reciprocating bar 398 which serves to drive the electrodesupporting cylinders. Thus, connected to the bar 398 and extendingupwardly therefrom is a link 450 which is pivoted at its upper end 451on a frame bracket 452. For interconnecting the arm 332 and the link 450a pushrod 453 is provided which is pinned to the arm at its forward end454. The connection is made resilient by coil spring 455 surrounding therod and which engages a slidable collar 456 pinned to the center of thelink 450. It will, therefore, be apparent that when the bar 398 is movedforwardly, pressure is exerted by the link 450 upon the spring 455 tomove the pushrod 453 in the forward direction so that the pail isengaged by the table, the ear is engaged by the centering pin positionwhile the switch 457 signals improper positioning, the

welding guns being disabled in either event as will be discussed inconnection with the control circuitry.

EAR CHECKING ARRANGEMENT In the exemplary apparatus, feeler means areprovided for checking the presence of ears on the pail upon transfer ofthe pail from the welding station. More specifically, feeler arms arepivoted to the frame in the checking station 65 and moved inwardlytoward the pail to engage the ears when the pail is raised by thepositioning member 100. Referring to FIGS. 19 and 20, the feeler armarrangement at the front and rear sides of the machine is shown indetail and it will be understood that the following description isapplicable to both. Thus, the arm 470 is pivoted at 471 to the frame ofthe machine. At its upper end the arm carries a pivoted finger 472having an ear engaging tip 473. For the purpose of adjusting thevertical position of the feeler member, the arm has two relativelyslidable portions including a carrier 474 and with the relative positionbeing adjustable by a control knob 475 which engages a nut 476 on thecarrier. For the purpose of biasing the feeler member 472, a spring isprovided, with the spring force being adjustable by means of a knob 478.Relative rocking movenient between the feeler member and the arm when anear is engaged is utilized to control a switch 480 as will be covered inconnection with a discussion of the control diagram FIG. 21.

For the purpose of rocking the arm forwardly to place the feeler memberin the path of upward movement of the pail, a cam 481 is provided on theshaft 120 engaged by a cam follower 482 which is pinned to the lower endof the carrier portion 474 of the arm. Thus, in a typical sequence itwill be understood that the arm is rocked radially inward toward thepail so that the tip 473 is in the path of movement of the ear.Continued upward movement of the pail by the positioning member causesthe spring to be compressed, with rocking movement of the feeler member472 accompanied by actuation of the switch 480. The pressure exerted bythe spring 477 is sufficient so that there is insurance that any earwhich passes the checking step will have a strength which is adequatefor all normal usage of the resulting pail although the checkingmechanism does not develop the full strength of the weld.

In order to hold the pail steady as it is acted upon by the feeler arms,a disc 490 is provided which is similar to that in the welding station.The disc is carried on a vertical shaft 491 slidably received in abushing 492 and urged in a downward direction by a coil spring 493.

The last station 66 is an idle station which may be employed to performan added operation on the pails thereby to increase the versatility ofthe machine. It includes a clamping disc 500 on a shaft 501 slidable ina bushing 502 and with the disc being biased downwardly by a spring 503.When the pail leaves the station 66 it is moved by the transfer memberonto the conveyor 150. A reciprocating-type pusher mechanism may beemployed to move pails laterally from the conveyor for reject purposes.

In the above discussion, it has been assumed that the mechanism has beenadjusted for one size of pail. Means are provided for accommodating themachine to pails of different heights by raising or lowering thesuperstructure 55. Conveniently, this may be accomplished by a heightadjusting drive including a motor 510 having an angular drive connection511 for rotating shafts 512, 513 which extend along the top of themachine. Such shafts rotate worm driven nuts 514, 515 which cooperatewith threaded jack screws 516, 517. It will be apparent, then, thatsimply rotating the motor in one direction or the other thesuperstructure may be moved upwardly and downwardly along way surfaces.As previously disclosed this does not effect the adjustment of therotary orienting mechanism because of thedouble parallelogram Iinkageemployed in the latter.

INTEGRATED CONTROL CIRCUIT While the sequence of operation of theweldingmachine will be understood in the general: way from, the precedingdiscussion of the structure, it S.-One of the features of the presentinvention that the variousfunctions are integrated in a novel fashionunder the control of a control circuit whichis set forth in simplifiedform in FIG. 21..T o insure proper timing of the'various functions weprefer to, usea multiple section cam switch which is coupled to the camshaft 83 at a l:l speed ratio. The cam switch is indicated generally inFIG. 2 by the numeral 530 and it may be conveniently driven by asuitable angular drive connection from the same chain l43,which servesto drive the conveyor 140. The various sections of the cam switch havebeen indicated in FIG. 21 at 531 539 inclusive.

Turning to FIG. 21, lines 551, 552 will be understood to be connected tothe regular commercial supply line. In series with the main drive motoris a switch or control 553. In series with the orienting motor 181 is asuitable switch 554. The motor 555 which drives the hoppers has acontrol switch 556. Finally, the adjusting motor 510 for adjustingheight of the structure, which is of the reversible type, has up" anddown" switches 557, 558. It will be understood that during the normaloperation, control switches 553, 554 and 556 will be closed and theswitches 557, 558 will be open so that the adjusting motor remains at aconstant adjustment.

As the cam shaft 83 rotates to drive the transfer and positioningmembers 70, 100, pails will be transferred simultaneously into all ofthe stations. Directing attention to the pail in the first orientingstation 61, the sections 531, 532 of the cam switch are closed, therebyclosing the circuit to a course orient" relay 560 having contacts 561,562, 563. The contacts 561 are normally open and connected in serieswith the clutch 175 while the contacts 562 are normally closed andconnected in series with the brake 176. The contacts 563 which arenormally open, serve the purpose of sealing in contacts and areconnected in series with the switch 194 controlled by the star wheel190. Because of the sealing in contacts, the relay 560 remains closed,energizing the clutch 175 to rotate the pail engaged by the disc 170.When the seam of the pail arrives, tripping the star wheel 190, theswitch 194 momentarily opens, dropping out the relay. This deenergizedthe clutch so that the seal is stopped with the seam thereonapproximately oriented in desired position.

Directing attention next to the pail in the fine orient" station 62,there is provided a relay 570 having contacts'571, 572 and 573. Theswitch 255 of the detector 250 is connected in series with the contacts573 which perform a sealing function. After a pail has been moved intothe orienting station 62, the section 533 of the cam switch is closed,picking up the relay 570 and energizing the clutch 175a. This producesrotation of the disc a at slow speed because of the stepdown gear driveshown in FIG. 8. When the slow-speed detector engages the seam of thepail, the switch 255 is opened dropping out the relay 570 whichdeclutches the drive and energizes the brake 17Gb to locate the pail ina precisely oriented position.

For the purpose of dropping ears into the welding station, theescapement 310 shown in FIG. 6, as stated, operated by two solenoids 314, 314a under the control of the sections 534, 535 of the cam switch.The timing of the cam switches is such that the two solenoids arenormally operated -in sequence. Thus, the solenoid 314 will be operatedto drop an ear, but before the next ear can be dropped the escapementmust be reset by operating the reload solenoid 314a. In accordance withone of the detailed features of the invention, the overtravel switch256, which is under the control of the slow-speed detector 250, isconnected in series with the reloadnsolenoid 3140. Consequently, thereload solenoid performs a memory function, i.e., no reloading of theescapement takes place to enable dropping of an ear in the succeedingcycle. To summarize, any overtravel of the pail in the final orientingstation opens the switch 256 to prevent reloading of the escapernent;consequently, when the misoriented pail reaches the next, or weldingstation, no cars will be dropped on either side of the pail forengagement by the gauge pins 331 to enable operation of the weldcontroller. The weld controller has beenindicated at 580.

Turning attention to the weld controller circuit, it will be noted thatthe switches 458, which are normally closed, and the switches 457, whichare normally open, associated with the gauge pins 331, are all connectedin series with the section 536 of the cam switch. Thus, the cam switch,when the remainder of the circuit is completed, normally acts toenergize the weld controller 580 to initiatethe welding. The nature ofthe weld controller, and the particular sequence of force and currentwhich is employed in the present invention will be covered in thefollowing section.

However, in carrying out the present invention and as far as the gaugepin switches are concerned, the absence of any ears in the weldingstation causes the pins to overtravel, thereby opening the normallyclosed switches 458 and preventing a circuit from being completed to theweld controller. In short, when no car drop takes place to a misorientedpail, the weld controller is effectively disabled so that no weldoccurs.

In the illustrative apparatus, means are provided for countingsuccessive pails found to lack ears in the checking station 65 and forshutting down the machine, or for notifying the machine operator, whenthe number of such successive pails reaches a predetermined total. Itwill be understood from the above that the lack of ears on a pail in thechecking station will most commonly be due to the fact that such pailwas not properly oriented thereby disabling ear drop reload solenoid314a. Thus, it is presumed that whena group of successive pails arefound to be without ears, the machine should be shut down untilappropriate adjustment may be made in the final orienting station. Toaccomplish automatic shutdown there is provided in the present device anear test relay 585 having normally open contacts 586 and normally closedcontacts 587. The relay 585 is connected in series with section 537 ofthe cam switch and the ear test switches 480 in the ear checking stationat opposite sides of the machine. The contacts 586, 587 are used tocontrol a counter 590 having a count line 591 and reset line 592.Connected in series with the reset line is section 538 of the camswitch.

The ear checking switches 480 are normally closed. Thus, in the eventthat a pail in the checking station lacks ears, switches 480 will remainclosed with the result that cycling of the cam switch section 537applies an impulse to the relay 585, picking up the relay to causeclosure of the normally open contacts 586 to register a count in thecounting circuit. To store the count, i.e., to prevent resetting of acounter upon deenergization of the relay 585, a latching relay 595 isemployed having a latch 596 which engages a cooperating latch member 597on the plunger of the relay 585. Thus, the relay 585 is, temporarily,prevented from dropping out to the point of closing the contact 587.

If the next pail to enter the checking station 65 is also without ears,the above operation will be repeated, i.e., .the relay 585 will beenergized to close the contacts 586, so that a second count isregistered in the counter. The counter may be a commercially availabledesign so that upon reaching a set count, output contacts are operated.The output contacts, in the present instance indicated at 598, are inthe form of normally closed contacts connected in series with thecontrol circuit for the main motor 90. Thus, when the desired count ofnoneared pails is reached, which may be five in a practical case, themain driving motor is shut off, bringing the machine to a halt andclearly signifying to the operator that an adjust-.

ment should be made before operation is continued.

However, when an cared pail is detected prior to the set count,resetting is effected by section 539 of the cam switch. Since the latteris in series with the latch relay 595, the latch 596 is withdrawn andcontacts 587 areclosed to apply a reset signal to the line 592 whichfeeds the counter.

In order to prevent the latching relay from producing unwanted reset,the on" time of the cam section 539 is made very short and is adjustedto fall within the .on time of the cam section 537. Thus, when a pailwithout cars is in the checking station, resulting in energization ofthe relay 585, the latching relay 595 will be momentarily energizedduring the time interval that the relay 585 is picked up. Because of theshortness of the time of energization of the latching relay, the latchwill fall back into latching position before the relay 585 becomesdeenergized. Briefly stated, while it is true that the latching relay595 is operated once each cycle, it is effective to unlatch the relay585, i.e., to permit it to drop out, only when there is an eared pail inthe checking station, since it is only then that the switches 480 areopened.

While the construction and operation of the counter 590 will be apparentto one skilled in the art from the foregoing description, it will beunderstood that we prefer to employ a counter of type I-IZ I50A60lmanufactured by Eagle Signal Co. and described in their Bulletin 725.

For the details of the program of the cam switch, reference is made toFIG. 21a which shows the on" time for the switch sections 53l-539employed in the case of a practical installation.

While the discussion has been directed toward the structural aspects ofthe welding machine, it is one of the important features of theexemplary apparatus and welding system to provide a specificrelationship between the structure and the specific force-current cyclewhich has been found to enable perfectly reliable welding through paint,lithographing, or other protective coating on thesurface of the pail. Asstated above, it is contemplated that the painting or lithographing willtake place while the pail is still in the flat condition, with thesurface being thoroughly covered so that no "bare spots" are availablefor making electrical contact.

We preferably employ a projection which is the result of a piercingoperation so as to produce a tapered relatively sharp edge of limitedcross section. A sectional view, taken through the projection andassociated base member (the wall of the pail) is set forth in FIG. 23a,the scale being greatly enlarged to facilitate understanding. Thus, theprojection indicated at 600, has a relatively sharp edge 601. In apractical case, such edge will not be smooth and continuous but on thecontrary will be ragged or sawtoothed to define a number of projectingpoints arranged in a circular locus. In the same FIG. the base memberhas been indicated at 605 and the coating thereon by the layer 606. Theprojection has a height from the surface of the attachment indicated athl. The welding electrodes 369, 371 previously discussed, and which areindicated by the dimension line in the FIG. preferably occupy an areawhich is substantially greater than the diameter of the projection, themajor diameter of the projection being indicated at dl and the minordiameter at d2.

In order to better understand the reasons for the effectiveness of thepresent apparatus and procedure in securing a sound weld through aninsulating coating a series of stop motion cross section views have beenprepared as set forth in FIGS. 23a-23b inclusive and which are keyed toa plot of projection height, pressure and current in a typical weldingcycle. The FIGS. are based upon actual. observations made in an effortto explain successive occurrences during the cycle.

FIG; 23a showsthe initial condition with the electrodes brought intolight contact with the work but with substantially zero force appliedand with the coating not yet penetrated.

Upon slight additional movement of the movable electrode,

the force applied rises rapidly as indicated at F 1. Since the spring ispreferably stiff having a prestress force of approximately 330 pounds,concentrated upon aprojection diameter d2 of only 0.040 inch, the sharpedge of the projection is forced through the coating to establish alimited area of electrical contact followed immediately by deformationor partial axial collapse of the projection to the condition shown inFIG. 23b and with the projection height being reduced to a value h2.That is, the sharp edge 601 is crushed and tends to spread out in bothradial directions, defining a reduced inner diameter d3 and an increasedouter diameter d4. The net effect is to substantially increase thecross-sectional area of the metal at the edge of the projection. Theinitial electrical contact made between the parts, for example, asindicated at 607, is maintained during the transition and, in thefollowing steps, the areas of electrical contact may even be enlargeddepending upon the nature of the coating material. It may be emphasizedat this point that advancement of the electrode 369 and the buildup offorce along the applied force curve takes place positively substantiallyfree of the effect of inertia or other transient effects whichcharacterize air actuators or the like commonly employed in weldingpractice. Thus, the transition between conditions of contact shown inthe stop motion views is progressive from the time that the initialelectrical contact is made to the time that the projection issubstantially flattened and free of any momentary release or reboundwhich might effeet the continuity of the electrical circuit.

As the spring 380 in the welding gun 351 is picked up, in other words,as the central rod 358 is unseated from the seat 382 in the gun, theforce exerted by the electrode 369 further increases, reaching a valueF2 (FIG. 22) accompanied by further deformation of the projection, withthe height being reduced to the value h3, the inner diameter beingreduced to the value d5 and the outer diameter being increased to thevalue d6. The contact areas 607 remain in engagement and some of thecoating material is trapped as indicated at 608.

At the end of the forward stroke of the gun actuating bar 398 (FIG.l4),-the throw of which is determined by the cams which drive it, thebar remains temporarily stationary to apply a high sustained forceto'the welding electrode having a value indicated at F3 in FIG. 22.Increase in force to the maximum value further deforms the projectionuntil it appears as set forth in FIG. 23d. Here it will be noted thatthe inner diameter of the projection has been reduced to the point wherethe projection is substantially closed. The contact is maintained andenlarged over areas 607 and pockets of coating material 608 become morewell defined.

Application of full welding current is delayed until after theprojection has been substantially deformed, that is, substantiallyflattened out as indicated in FIG. 230 or FIG. 23d. Thus the current ispreferably turned on at point 01, i.e., after a delay time 11 from thestart of the welding cycle which may be in the order of one-twenthiethsecond. This timing is achieved in the present instance, by the phase ofsection 536 of the cam switch which is in series with the input to thewelding controller. However, as the discussion proceeds it will beapparent to one skilled in the art that such delay need not be securedby a timed switch and that, if desired,'the current may be initiated byswitch which is responsive to the buildup of the force applied by theelectrode 369 and spring 380.

The current, when applied, is not applied at full welding -value butmeans are provided within. the welding controller 580 for causing thecurrent to buildup from a reduced value 01 or less linearly along acharacteristic curve c2 to a final value c3. Such buildup of current ina practical case may take place over an interval :2 on the order ofone-tenth second in length. Welding controllers capable of such -upslopewith variable rise time are commercially available.

Current and force are both thereafter maintained at the values 03, F3,respectively, which may be in the order of 9,000 amperes and 350 pounds,over a further interval :3 which may be on the order of 0.25 second. Theheating which takes place during this time interval produces atemperature which is suftrained coating material is decomposed and isfound not to affect the soundness of the weld.

It is found that by using the above procedure, flashing, i.e., theburning away of the projection, is completely eliminated and that eachweld is sound and homogeneous notwithstanding the insulating paint orother coating. Observations show that the elimination of flashing is dueinput to the deformation of the thin tapering edge of the projectionfrom the thin initial cross section to substantially thicker crosssection before the application of current without interrupting thecontinuity of the contact originally made and with substantial increasein the thermal coupling between the projection and the relativelymassive pieces of metal lying on the opposite sides of the projection.Because of the increase in cross section and the close thermal couplingexcess localized heat is promptly conducted away so that there is nopossibility of temperature buildup in the projection to the level atwhich burning or flashing away may occur. Localized buildup of heat inthe projection is also minimized by the fact that the electrodes, bothmovable and fixed, constitute an efficient heat sink.

The continuous maintenance of electrical contact from the moment ofinitial contact by the points of the projection is also believed to be acontributing factor. As stated, such contact is maintained by reason ofthe fact that the electrodes are advanced positively and progressivelywithout being affected by inertia effects or rebound. Moreover, use of apierced projection tends to produce a scrapingaction as the projectionis deformed, with part of the edge scraping inwardly to reduce a minimumdiameter of the projection and the remainder scraping outwardly toincrease the maximum diameter. Where such a projection is used and wherethe parts are put through a pressure cycle without application of thewelding current, it is found that the insulating coating tends to besubstantially cleared from a small but rather well-defined annular area.This scraping action is, however, to be distinguished from the scrapingwhich might occur due to bodily deformation of the car being attached.In the present procedure deformation is limited to the projectionitself.

After the welding current has been applied the additional time 13 thecurrent is cut off as shown in FIG. 21 but force continues to be appliedfor an additional time interval 14 to permit the weld to cool and remainintact when the force on the welding electrodes is released.

It is particularly noteworthy that all of .the above occurs within anextremely short period of time, on the order of onehalf second and itis, indeed, one of the features of the present machine that in spite ofthe sequential action production rates are obtainable which arecomparableto or even higher than where conventional bare metalweldingtechniques are emv ployed.

While a pierced projection has been described as the preferredembodiment, it will: be understood that other specific shapes ofprojections may be employed having a relatively sharp edge forpenetrating a coating, where .the edge is either continuous or localizedin the form of a point and where deformation of the edge occurs toincrease the cross section and hence the thermal coupling uponapplication of force and prior to the application of the full weldingcurrent.

We claim:

1. In a welding machine for welding ears having a bail opening centeredtherein to a metal pail, the combination comprising, a welding stationhaving means for supporting a pail, means for feeding an ear adjacentthe wall of said pail and in approximate position for welding thereto, atapered centering pin generally aligned with the opening in theear andmounted for movement with respect thereto, fixed electrode inside ofsaid pail and movable electrode cooperating therewith adjacent said ear,means for moving the centering pin and the movable electrode so that thetapered end of the centering pin is received within the opening of theear for precise centering of the ear with respect to the pail and sothat the movable electrode is subsequently brought into bottomingcontact with the ear against the electrode, means for supplying currentto the electrode following contact between the movable electrode and theear, and means responsive to excessive inward movement of the centeringpin indicative of the absence of the ear for disabling the currentsupply means.

2. In a welding machine for welding an attachment to a base member, thecombination comprising, a machine frame, means for supporting the basemember on said frame, means for feeding an attachment relative to thebase member to position the attachment adjacent the base member, awelding circuit including a pair of welding electrodes mounted on saidframe, at least one of said electrodes being movable relative to thebase member and being disposed opposite a welding surface on theattachment when the latter is properly positioned adjacent the basemember, locator means mounted on said frame for selective relativemovement towards and away from the attachment and the adjacent basemember for accurate final positioning of the attachment relative to thebase member, means for advancing said locator means and said movableelectrode relative to the attachment and the adjacent base member sothat said locator means engages the attachment and accurately positionsthe attachment on the base member and so that said electrode engages thewelding surface on the attachment to enable said welding circuit,detecting means mounted on said frame for sensing the position of saidlocator means relative to the base member, and means for applyingcurrent to said electrodes for welding the attachment said currentapplying means in response to the position of said I locator meansrelative to the base member.

3. The combination as set forth in claim 2 further characterized in thatsaid disabling means is rendered'operative upon detection of excessiverelative closing movement of said locator means and the base memberindicative of the absence of an attachment.

4. The combination as set forth in claim 2 further characterized in thatsaid disabling means is rendered operative upon detection ofspacingbetween the base member and said locator means greater than apredetermined spacing indicative of improper orientation of theattachment relative to the base member.

5. The combination as set forth in claim 6 further characterized in thatsaid enabling means is rendered operative only upon detection of apredetermined spaced condition of said locator means relative to thebase member indicative of 1) the presence of an attachment, and 2) acondition of proper preselected orientation of the attachment relativeto the base member. I

6. In a welding machine for welding an -attachment to a base member, thecombination comprising, a machine frame, means for supporting the basemember on said frame, means for feeding an attachment relative to thebase member to position the attachment adjacent the base memberincluding a chute for delivering the attachment in an orientedcondition, a welding circuit including a pair of welding electrodesmounted on said frame, at least one of said electrodes being movablerelative to the base member and being disposed opposite a weldingsurface on the attachment-when the latter is properly positionedadjacent the base member, locator means mounted on said frame forselective relative movement towards and away from the attachment and theadjacent base member for accurate final positioning of the attachmentrelative to the base member including an attachment supporting memberand a pair of gates for holding the attachment adjacent the base memberin its oriented condition, said gates being relieved to form acontinuation of said chute, means for advancing said locator means andsaid movable electrode relative to the attachment and the ad acent basemember so that said locator means engages the attachment and accuratelypositions the attachment on the base member and so that said electrodeengages the welding surface on the attachment to enable said weldingcircuit, and means for applying current to said electrodes for weldingthe attachment to the base member in its desired position.

7. The combination asset forth in claim 6 further characterized in thatsaid means for advancing said movable electrode is operable tosimultaneously retract said gates to an out-of-the-way position forpositive bottoming contact between said movable electrode and theattachment.

8. In a welding machine for welding an attachment to a base member, thecombination comprising, a machine frame, means for supporting the basemember on said frame, means for feeding at least two attachmentsrelative to the base member to position the attachments at spaced pointsadjacent the base member, a welding circuit including at least twowelding electrodes mounted on said frame, said electrodes being movablerelative to the base member and being respectively disposed opposite awelding surface formed on each of the attachments when the latter areproperly positioned adjacent the base member, locator means mounted onsaid frame for selective relative movement towards and away from theattachments and the adjacent base member for accurate final positioningof the attachments relative to the base member, means for advancing saidlocator means and said movable electrodes relative to the attachmentsand the adjacent base member so that said locator means engages theattachments and accurately positions the attachments on the base memberand so that said electrodes engage the respective welding surfaces onthe attachments to enable said welding circuit, detecting means mountedon said frame for sensing the position of said locator means relative tothe base member, and means for applying current to said electrodes forsimul taneously welding the attachments to the base member in theirdesired position, said detecting means including means for selectivelyenabling and disabling said current applying means in response to theposition of said locator means relative to the base member.

9. The combination as set forth in claim 8 further characterized in thatsaid disabling means is rendered operative upon detection of excessiverelative closing movement of said locator means and the base memberindicative of the absence of at least one of the two attachments so asto thereby preclude welding of only one attachment to the base member.

10. The combination as set forth in claim 8 further characterized inthat said disabling means is rendered operative upon detection ofspacing between the base member and said locator means greater than apredetermined spacing indicative of improper orientation of at least oneof the two attachments relative to the base member was to therebypreclude the welding of both the misoriented attachment and any properlyoriented attachment to the base member.

11. The combination as set forth inclaim 8 further characterized in thatsaid enabling means is rendered operative only upon detection of apredetermined spaced condition of said locator means relative to thebase member indicative of l) the presence of both attachments, and 2) acondition of proper preselected orientation of both attachments relativeto the base member.

1. In a welding machine for welding ears having a bail opening centeredtherein to a metal pail, the combination comprising, a welding stationhaving means for supporting a pail, means for feeding an ear adjacentthe wall of said pail and in approximate position for welding thereto, atapered centering pin generally aligned with the opening in the ear andmounted for movement with respect thereto, fixed electrode inside ofsaid pail and movable electrode cooperating therewith adjacent said ear,means for moving the centering pin and the movable electrode so that thetapered end of the centering pin is received within the opening of theear for precise centering of the ear with respect to the pail and sothat the movable electrode is subsequently brought into bottomingcontact with the ear against the electrode, means for supplying currentto the electrode following contact between the movable electrode and theear, and means responsive to excessive inward movement of the centeringpin indicative of the absence of the ear for disabling the currentsupply means.
 2. In a welding machine for welding an attachment to abase member, the combination comprising, a machine frame, means forsupporting the base member on said frame, means for feeding anattachment relative to the base member to position the attachmentadjacent the base member, a welding circuit including a pair of weldingelectrodes mounted on said frame, at least one of said electrodes beingmovable relative to the base member and being disposed opposite awelding surface on the attachment when the latter is properly positionedadjacent the base member, locator means mounted on said frame forselective relative movement towards and away from the attachment and theadjacent base member for accurate final positioning of the attachmentrelative to the base member, means for advancing said locator means andsaid movable electrode relative to the attachment and the adjacent basemember so that said locator means engages the attachment and accuratelypositions the attachment on the base member and so that said electrodeengages the welding surface on the attachment to enable said weldingcircuit, detecting means mounted on said frame for sensing the positionof said locator means relative to the base member, and means forapplying current to said electrodes for welding the attachment to thebase member in its desired position, said detecting means includingmeans for selectively enabling and disabling said current applying meansin response to the position of said locator means relative to the basemember.
 3. The combination as set forth in claim 2 further characterizedin that said disabling means is rendered operative upon detection ofexcessive relative closing movement of said locator means and the basemember indicative of the absence of an attachment.
 4. The combination asset forth in claim 2 further characterized in that said disabling meansis rendered operative upon detection of spacing between the base memberand said lOcator means greater than a predetermined spacing indicativeof improper orientation of the attachment relative to the base member.5. The combination as set forth in claim 6 further characterized in thatsaid enabling means is rendered operative only upon detection of apredetermined spaced condition of said locator means relative to thebase member indicative of 1) the presence of an attachment, and 2) acondition of proper preselected orientation of the attachment relativeto the base member.
 6. In a welding machine for welding an attachment toa base member, the combination comprising, a machine frame, means forsupporting the base member on said frame, means for feeding anattachment relative to the base member to position the attachmentadjacent the base member including a chute for delivering the attachmentin an oriented condition, a welding circuit including a pair of weldingelectrodes mounted on said frame, at least one of said electrodes beingmovable relative to the base member and being disposed opposite awelding surface on the attachment when the latter is properly positionedadjacent the base member, locator means mounted on said frame forselective relative movement towards and away from the attachment and theadjacent base member for accurate final positioning of the attachmentrelative to the base member including an attachment supporting memberand a pair of gates for holding the attachment adjacent the base memberin its oriented condition, said gates being relieved to form acontinuation of said chute, means for advancing said locator means andsaid movable electrode relative to the attachment and the adjacent basemember so that said locator means engages the attachment and accuratelypositions the attachment on the base member and so that said electrodeengages the welding surface on the attachment to enable said weldingcircuit, and means for applying current to said electrodes for weldingthe attachment to the base member in its desired position.
 7. Thecombination as set forth in claim 6 further characterized in that saidmeans for advancing said movable electrode is operable to simultaneouslyretract said gates to an out-of-the-way position for positive bottomingcontact between said movable electrode and the attachment.
 8. In awelding machine for welding an attachment to a base member, thecombination comprising, a machine frame, means for supporting the basemember on said frame, means for feeding at least two attachmentsrelative to the base member to position the attachments at spaced pointsadjacent the base member, a welding circuit including at least twowelding electrodes mounted on said frame, said electrodes being movablerelative to the base member and being respectively disposed opposite awelding surface formed on each of the attachments when the latter areproperly positioned adjacent the base member, locator means mounted onsaid frame for selective relative movement towards and away from theattachments and the adjacent base member for accurate final positioningof the attachments relative to the base member, means for advancing saidlocator means and said movable electrodes relative to the attachmentsand the adjacent base member so that said locator means engages theattachments and accurately positions the attachments on the base memberand so that said electrodes engage the respective welding surfaces onthe attachments to enable said welding circuit, detecting means mountedon said frame for sensing the position of said locator means relative tothe base member, and means for applying current to said electrodes forsimultaneously welding the attachments to the base member in theirdesired position, said detecting means including means for selectivelyenabling and disabling said current applying means in response to theposition of said locator means relative to the base member.
 9. Thecombination as set forth in claim 8 further characterized in that saiddisabling means is rendered operative upon detection of excessiverelaTive closing movement of said locator means and the base memberindicative of the absence of at least one of the two attachments so asto thereby preclude welding of only one attachment to the base member.10. The combination as set forth in claim 8 further characterized inthat said disabling means is rendered operative upon detection ofspacing between the base member and said locator means greater than apredetermined spacing indicative of improper orientation of at least oneof the two attachments relative to the base member so as to therebypreclude the welding of both the misoriented attachment and any properlyoriented attachment to the base member.
 11. The combination as set forthin claim 8 further characterized in that said enabling means is renderedoperative only upon detection of a predetermined spaced condition ofsaid locator means relative to the base member indicative of 1) thepresence of both attachments, and 2) a condition of proper preselectedorientation of both attachments relative to the base member.